Collated screwstrips are known in which the screws are connected to each other by a holding strip of plastic material. Such strips are taught, for example, by U.S. Pat. No. 4,167,229 issued Sep. 11, 1979 and its related Canadian Patents 1,040,600 and 1,054,982 as well as U.S. Pat. No. 4,930,630, the disclosures of which are incorporated herein by reference. Screws carried in such screwstrips are adapted to be successively incrementally advanced to a position in alignment with and to be engaged by a bit of a reciprocating, rotating power screwdriver and screwed into a workpiece. In the course of the bit engaging the screws and driving it into a workpiece, the screw becomes detached from the plastic holding strip leaving the strip as a continuous length.
In the use of such collated screwstrips in screwdrivers, the strip serves a function of assisting in guiding the screw into a workpiece and, to accomplish this, the holding strip is retained against movement towards the workpiece. In the screwstrip, each screw to be driven has its threaded shaft threadably engaged in a threaded sleeve of the holding strip such that on the screwdriver engaging and rotating each successive screw, the screw turns within the sleeve which acts to guide the screw as it moves forwardly into threaded engagement into the workpiece. Preferably, only after the tip of the screw becomes engaged in the workpiece, does the head of the screw come into contact with the sleeves. Further, forward movement of the screw into the workpiece then draws the head downwardly to engage the sleeve and to rupture the sleeve by reason of the forward movement of the head with the strip retained against movement towards the workpiece. The sleeve preferably is configured to have fragile straps which break on the head passing through the sleeve such that the holding strip remains intact as a continuous length. Since the holding strip is a continuous length, on advancing the screwstrip with each successive screw to be driven, it necessarily results that portion of the holding strip from which each screw has been driven are also advanced to exit from the power screwdriver.
Known power screwdrivers for driving such collated screwstrips include U.S. Pat. No. 4,146,071 to Mueller et al, issued Mar. 27, 1976, and U.S. Pat. No. 5,186,085 to Monacelli, issued Feb. 16, 1993, the disclosure of which are incorporated herein by reference. Such known power screwdrivers include a rotatable and reciprocally moving screwdriver shaft which is turned in rotation by an electric motor. A screwdriving bit forms a forwardmost portion of the shaft for engaging the head of each successive screw as each screw is moved into a driving position, axially aligned under the screwdriver shaft.
Known power screwdrivers for collated screwstrips suffer the disadvantage appreciated by the applicant that they are dedicated to drive collated screws. In use, they cannot be used to drive separate screws or to withdraw mis-driven screws or other screws which are desired to be removed. Known power screwdrivers for collated screwstrips also suffer the disadvantage that it is difficult to engage and change bits mounted to the front end of the drive shaft.